1. Field of the Invention
The present invention relates to a signal recording apparatus and, more particularly, to a signal recording apparatus arranged to record an index signal together with a main information signal by means of rotary heads.
2. Description of the Related Art
A video tape recorder (VTR) based on a so-called 8 mm video system is known as one rotary-head helical scan type of recording and reproducing apparatus. In such an 8 mm VTR, two magnetic heads having different azimuth angles are spaced apart through 180.degree. around the circumferential surface of a rotary drum, and a magnetic tape is slantwise scanned alternately by the magnetic heads so that video signals are recorded in sequence.
FIG. 1 shows a recording format of the 8 mm video system. A PCM audio signal recording area AP is formed over 36.degree. from the leading end of a track at which either of the magnetic heads comes in abutment with the magnetic tape, and a video signal recording area AP is formed over the next 185.degree.. The initial 5.degree. of the PCM audio signal recording area AP is a portion in which the magnetic head starts track scanning. The first 2.94.degree. of this portion is a start-of-scan area and the second 2.06.degree. (equivalent to 3H; 1H is one horizontal scanning period) is a preamble for clock run-in to establish synchronization with the succeeding PCM data. After the preamble, a recording area for PCM data on a timebase compressed audio signal is formed over 26.32.degree.. Then, a postamble serving as a back margin for the offset of a recording position or the like during postrecording is formed over 2.06.degree. (3H), and a guard area is formed over 2.62.degree.. Following the guard area, a recording area for one field of video signals is formed over 180.degree., and then an end-of-scan area is formed over 5.degree..
One field of audio data and index data including time information, cueing information, etc., on the audio data are time-base-multiplexed so that these data are recorded in the PCM data area with the index data mixed with the audio data. The index data includes various data such as the year, month and day of recording, an absolute address, a program number, time information (a so-called time code) and cueing information, and is used for cueing or editing during reproduction.
However, since the index data is interleaved with the audio data and recorded in coded form, it is impossible to take out the index data before the PCM data is de-interleaved and decoded. Accordingly, there has conventionally been the problem that a long processing time is taken until the index data becomes available for cueing or editing. An additional problem is that, during search reproduction, it is difficult to reproduce the index data correctly since recording tracks are slantwise scanned by the rotary heads.
To cope with the above-described problems, a method has been proposed in which index data having contents similar to the index data contained in the PCM data is recorded in the postamble area of the PCM audio signal recording area AP.
FIG. 2 shows the index format of the postamble area in this method. As shown in Part (a) of FIG. 2, the postamble area following the PCM data area is assigned 2.65H, and the succeeding 1.5H is assigned to an index area. The guard area is assigned 2.65H.
As shown in Part (b) of FIG. 2, in the index area of 1.5H, the first 1.26H is a header area and the second 0.24H is a coding-data area. If an index signal is recorded in this index area, "0" is written to the header area repeatedly and continuously. If an index signal is not recorded or has been erased, "1" is written repeatedly and continuously. The coding-data area is divided into eight blocks as shown in Part (c) of FIG. 2. A code start marker is placed in the first block, an 8 bit ID code in each of the succeeding five blocks, a CRC code for error detection in the next block, and a code end marker in the last block.
The above-described method has the advantage that since the index data is recorded in an area different from the PCM data area, only the index data can be independently recorded in a recorded track at a later time.
However, in the aforesaid index format, to realize an accurate picture search, for example, on a picture-by-picture basis, captures, frame numbers and the like must be continuously recorded from the leading edge of a tape over the coding-data areas of individual index areas. In addition, since it is necessary that "0" in the header can be reliably reproduced during search reproduction, "0" must be recorded in each track continuously over at least a predetermined area, and continuously for a predetermined time or more (for example, 10 seconds). A fine search is, therefore, impossible.